IOO 
thk story or thr oak tree; 
million worms; they will eat almost anything they can 
get their skins over, so that in one acre of ground they 
pass ten tons of soil through their bodies every year. 
They have been doing this for millions of years; every 
bit of soil on the surface of the earth has passed through 
their bodies many times. 
Darwin found that the worms work chiefly by night, 
when he would see hundreds of them, “with tails fixed in 
their burrows, prowling round in circles,” and strongly 
resisting any effort to pull them out. “An age-long 
ploughing field which was so thickly covered with hard 
flints that it was known as ‘the stony field’ was left un¬ 
touched for thirty years, after which a horse could 
gallop from one end to another without ever striking a 
stone.” 
All his life Darwin continued this patient study, and 
when he was seventy-two, the year before he died, he 
published a book which proves that earthworms have 
made most of the fertile soil of the world. 
“When we behold a wide, turf-covered expanse,” wrote 
Darwin—I have changed one or two of his words—“we 
should remember that its smoothness, on which so much 
of its beauty depends, is mainly due to all the unevenness 
having been slowly leveled by worms. How marvelous 
to know that the whole of the top soil over any such ex¬ 
panse has passed, and will soon pass, every few years 
